100% Test Coverage, Still Wrong — Mutation Testing (with Typescript) for Real Confidence скачать в хорошем качестве

100% Test Coverage, Still Wrong — Mutation Testing (with Typescript) for Real Confidence

I’m going to show how mutation testing turns 100% coverage from a vanity metric into real confidence, by catching the bugs your tests currently miss. In this TypeScript + Vitest + React walkthrough, I start with 100% code coverage, introduce tiny real-world faults (the kind LLM-assisted coding can slip past), and use Stryker to expose missing business rules, edge cases, and defensive code you can delete. What you’ll learn • Why 100% coverage can be useful when doing proper TDD (design pressure, safe refactors), but not sufficient • How LLMs can easily produce green tests with weak assertions—and how mutants reveal it • A practical triage loop: we look at missing requirements, edge cases, and examples where we can delete code • Thoughts on how I'm going to use this on my personal project moving forward, and how you might consider using it in your projects Highlights from my codebase • 100% Code Coverage ✅ • 81.28% Mutation Score ⚠ • 137 Surviving Mutants → real gaps to fix Sign up to my newsletter and keep visiting as I start adding articles to the site: https://feedbackdriven.dev